1. Field
The invention is in the field of processes for recovering dissolved metal values from solutions containing same, especially etching solutions.
2. State of the Art
There are many known processes for recovering dissolved copper values from solutions containing same. Most of these are concerned with the recovery of copper values from pregnant leach solutions derived by leaching sulfide copper ore materials with a weak sulfuric acid lixiviant. The most commonly employed process in this connection is the so-called "cementation" of metallic copper on metallic iron employed as a precipitant, followed by pyrometallurgical and electrolytic purification of the precipitated copper. However, electrowinning of dissolved copper directly from such pregnant leach solutions has also been employed, though that is not normally an economic procedure. A process which has received considerable attention recently in connection with the recovery of copper values from ammoniacal leach solutions involves liquid-liquid extraction of the copper values, utilizing a so-called "LIX" reagent produced by General Mills Chemicals, Inc., followed by electrowinning of metallic copper from the aqueous, acidic, stripping solution.
Solutions containing copper values are produced when metallic copper is subjected to the etching action or alkaline etching solutions. Efforts have been made in the past to remove the dissolved copper values from spent etching solutions, either to regenerate such solutions for reuse or to recover the metal values or both. An example of such a process, as applied to spent chromic acid etching solutions derived from the manufacture of printed electronic circuit boards, is that disclosed by U.S. Pat. No. 3,531,262 issued to Robert R. Dougherty on Sept. 29, 1970 for "Treatment of Used Chromic Acid Etching Solutions by Extraction With Acetone". But, so far as we are aware, there has heretofore been no commercially feasible, similar process for removing and recovering dissolved copper values from ammoniacal etching solutions, which solutions differ from other pregnant ammoniacal solutions in that they contain chlorides. we have found that the presence of chloride ions in an electrolyte is dangerous, because of the evolution of chlorine gas during electrolysis.
Considerable quantities of copper-containing, ammoniacal etching solutions are sent to waste by manufacturers of printed electronic circuit boards despite recognition by the art that it is advantageous to regenerate etching solutions and recover the etched copper values therefrom. This has created pollution problems and considerable expense for etching solution. Although in some instances copper values have been precipitated from such solutions with lime, as copper oxides, and have been used in food processing and wood treating industries, this has not proven to be an entirely satisfactory solution to the problems presented.